An Underground Ally for Sugar
Beets?

A new kind of soil bacteria found living around sugar beet roots may offer a
natural defense against fungi that menace the crop. Grown on 1.5 million acres,
sugar beets supply roughly 50 percent of the nations sucrose.

Agricultural Research Service
microbiologist David Kuykendall is investigating the bacterias potential
as a fungicide alternative in studies at the ARS
Molecular Plant Pathology
Laboratory (MPPL) in Beltsville, Md. In early findings from a series of
petri dish experiments, colonies of two Pseudomonas bacteria exuded
substances that curbed the growth of Cercospora beticola, a fungal rival
that lives on the plant's leaves.

Cercospora causes a rapid, progressive disease called leaf spot that
can defoliate susceptible sugarbeet cultivars. Fueled by humid conditions,
severe outbreaks can reduce sucrose yields by more than 30 percent. Growers
sometimes spray chemical fungicides when spots cover 3 percent of the
leaves surface. With fungicide use, however, comes legitimate concern
over the chemicals effectiveness due to the emergence of new,
fungicide-tolerant Cercospora strains, notes Kuykendall.

As an alternative, he envisions spraying the soil bacteria directly onto the
crops leaves when conditions are ripe for Cercospora outbreaks.
The Pseudomonas bacteria, two strains labeled ND6-2 and ND9L, were
obtained by ARS researchers Garry Smith and John Eide in North Dakota from the
rhizosphere, or soils around sugarbeet roots.

Now, Kuykendall is conducting plant host studies to learn whether either
strain poses any danger to other crops. By analyzing their DNA sequences, for
example, Kuykendall has identified a high degree of genetic similarity to
another Pseudomonas bacterium, P. corrugata, a tomato plant
pathogen. Results confirming the bacterial strains virulence would
probably rule out their use as a foliar spray. In that event, Kuykendall plans
an alternative strategy: isolate specific genes that give rise to their
anti-fungal secretions, and insert the bacterial genes into sugar beet. He
described the new findings in a recent issue of Sugar Journal.